I have done a couple of Fiats in the last year or so at work with ABS faults, and both times they have had the wiring corrode inside the insulation. On a Doblo van I had to pull the loom from the rear sensor, all the way back to the connection at the A pillar (had hi-resistance in the rear loom from the connector) and take off all the insulation all the way along and check the wire. Someone else had fitted a sensor and it still had the same fault.

Once I'd taken the braiding and tape off to expose the wires themselves, I found a cut in the wire, about 12" from the rear sensor connection. It had gone green with corrosion and snapped in my fingers.

I think when the looms are made they are in a jig with 'claws' to locate the loom on the jig, when the loom is pulled about, it can nick the insulation, and even though it's all taped up, moisture gets in there eventually and corrodes the wires.

In my experience, if the sensor has failed it will bring the light on as soon as you drive it.

My advice would be to get the sensor loom checked properly before just banging a sensor on it.